Michael Calderbank reports from the central London rally for Jeremy Corbyn

Jeremy Corbyn speaks from the top of the FBU’s fire engine to supporters who couldn’t get in to the oversubscribed rally.

It’s a cliche of the left press to describe meetings as ‘packed’. But the rally in support of Jeremy Corbyn’s Labour leadership bid held last night at the Camden Centre was really something else. Not only was the main hall packed to (and beyond) capacity, but so were both overspill rooms. Corbyn addressed hundreds left queuing outside from the FBU’s campaigning fire-engine. Similar scenes had been witnessed at the weekend in Liverpool, Preston and Birmingham. No wonder the Blairites are panicking. A genuine popular movement is beginning to coalesce around the bid to get Jeremy elected, and it senses that – for the first time in a generation – real change is possible.

The rally – chaired, significantly by PCS General Secretary Mark Serwotka, not himself a Labour party member – had more of the flavour of a People’s Assembly gathering than your usual Labour party meeting. It’s clear that the campaign is successfully appealing to a generation of activists whose political consciousness was shaped by the experience of New Labour in government – introducing student fees, deregulating the banks, invading Iraq. Most feel they have never been represented in the political process, but now see a chance to change all that. Corbyn was one of only a handful of MPs who really gave expression to their ideas then, and has been a rare voice in support of radical opposition to the austerity agenda ever since.

They are joined by an older layer of activists who recognise Corbyn’s ongoing commitment to internationalism, anti-racism, peace, and in defence of LGBT rights which were routintely depicted as ‘loony left’ in the 1980s, but which seem far from marginal or extreme today.

It’s also a revolt from below of the long-suffering Labour grassroots. Such has been the centralisation of power – with the manifesto being essentially the product of the leader and their special advisers with a cursory nod in the direction of the largely toothless National Policy Forum – that the opportunity to elect a new leader is pretty much the sole way that members have of trying to influence the political direction for the party. For years, the MPs acted as gatekeepers to keep the left challenge posed by John McDonnell off the menu. The pent up anger and frustration is finally getting expression. In his address to the rally, Corbyn pledged to end the culture of policymaking in the private surrounds of luxury hotels where debate was placed in the straitjacket of ‘consensus’, and talked about mass participation in genuine political debate. It was a breath of fresh air.

This is an insurgency from both within Labour – a revolt from below of the grassroots – and without. The Collins reforms which turned the Labour’s internal election into a semi-open primary has unexpectedly created an opportunity to crack the ossified politics of the Westminster establishment wide open. If Owen Jones’ tubthumping rhetoric can sometimes seem a little bit forced, last night it really hit the mark. Win or lose, something significant is being expressed in the huge wave of support for Corbyn.

The challenge will be to allow this spontaneous movement to coalesce into a political force which is organised, genuinely rooted in communities at local level and properly democratic in its structures. But with registration closing on August 12, the immediate priority is to encourage friends, neighbours, family and work colleagues to sign up and make sure that our voices are heard.